I am a Raptors fan and I think the Kings got an absolute steal. The only reason JJ was traded was because of a backlog at the SF spot, and a situation where he was the odd man out (due to Linas Kleiza being kept to solidify a good relationship with Jonas Valanciunas coming next season). He was the statistically the best defender on a decent defensive team with the Raps.
After reading these posts, it has become evident that many people think his shooting is poor, and while that may be true, in his 2 years with the Raps his shooting improved tremendously (he worked with a shooting coach practically every day). He is still only 24, and in a few years, he could be an amazing 6-7th man off the bench. Like a sparkplug almost. But that is the thing. He is no starting SF. Still probably better than any 2nd rounder you are gonna get, but he is no starter.
One thing Kings fans should know is that he had a problem with the Toronto coach (Dwane Casey) and got benched for maybe 3 games. Apparently it was nothing too serious and Casey over reacted to make an example out of him because of a few other incidents where younger players acted out. Casey said that all was well and spoke praises of JJ, but still, problems with coaches is never good.